Abstract
Ultra-thin Silicon Nanowires (SiNWs) were produced by means of an industrial inductively-coupled plasma (ICP) based process. Two families of SiNWs have been identified, namely long SiNWs (up to 2–3 micron in length) and shorter ones (~100 nm). SiNWs were found to consist of a Si core (with diameter as thin as 2 nm) and a silica shell, of which the thickness varies from 5 to 20 nm. By combining advanced transmission electron microscopy (TEM) techniques, we demonstrate that the growth of the long SiNWs occurred via the Oxide Assisted Growth (OAG) mechanism, while the Vapor Liquid Solid (VLS) mechanism is responsible for the growth of shorter ones. Energy filtered TEM analyses revealed, in some cases, the existence of chapelet-like Si nanocrystals embedded in an otherwise silica nanowire. Such nanostructures are believed to result from the exposure of some OAG SiNWs to high temperatures prevailing inside the reactor. Finally, the intense photoluminescence (PL) of these ICP-grown SiNWs in the 620–950 nm spectral range is a clear indication of the occurrence of quantum confinement. Such a PL emission is in accordance with the TEM results which revealed that the size of nanostructures are indeed below the exciton Bohr radius of silicon.
Highlights
One dimensional (1D) nanostructures have shown remarkable optical, electronic and chemical properties with respect to the bulk counterparts, because of the occurrence of both quantum confinement (QC) phenomena and surface effects[1]
The statistical analysis on several hundreds of nanostructures observed by EFTEM has allowed to determine that the diameter of the Si nanospheres (SiNSs) core is in the 45–480 nm range and they are surrounded by a ~8 ± 2 nm thick silicon oxide shell
This configuration will be referred to as “chapelet-like” silicon nanowires (SiNWs) hereafter. Their crystalline nature is ascertained by High Resolution transmission electron microscopy (TEM) (HRTEM) analyses, as shown in the inset of Fig. 2b, where a Si nanocrystals (SiNCs) in the zone axis is depicted
Summary
Silicon Nanowires and their associated photoluminescence received:13January2016 accepted: 28 October 2016 properties Published: 22 November 2016. The intense photoluminescence (PL) of these ICP-grown SiNWs in the 620–950 nm spectral range is a clear indication of the occurrence of quantum confinement Such a PL emission is in accordance with the TEM results which revealed that the size of nanostructures are below the exciton Bohr radius of silicon. Some OAG SiNWs exhibit an interesting inner structure, composed of well separated spherical Si nanocrystals (SiNCs) with a “chapelet-like” nanostructure or a string of “almond-shaped” SiNCs connected by a very thin SiNW, all embedded in a silica nanocylinder In this case, the inner SiNW is very thin, with diameter as thin as ~2 nm, while the silica outer shell was found to have a thickness ranging from 4 to 6 nm. The visible to near-infrared broad photoluminescence of these ICP-SiNWs is shown to correlate well with their TEM revealed nanostructural characteristics, supporting thereby the occurrence of quantum confinement in these silicon nanostructures
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